A fuel system is the component of an internal combustion engine which often has the greatest impact on performance and cost. Accordingly, fuel systems for internal combustion engines have received a significant portion of the total engineering effort expended to date on the development of the internal combustion engine. For this reason, today's engine designer has an extraordinary array of choices and possible permutations of known fuel system concepts and features.
Since the invention of the gasoline engine various attempts aimed at improving the efficiency of fuel systems have been made. Design effort typically involves extremely complex and subtle compromises among considerations such as cost, size, reliability, performance, ease of manufacture, and retrofit capability on existing engine designs. The challenge to contemporary designers has been significantly increased by the need to respond to government mandated emissions abatement standards while maintaining or improving fuel efficiency.
It is well known in the prior art to provide fuel in a liquid phase to a moving air stream for delivery to an internal combustion engine. Liquid fuel delivery systems, such as carburetors, were once standard for internal combustion engines. Carburetors use atomizing nozzles or jets which at least partially atomize the liquid fuel supplied to the engine. The nozzles aim the fuel at the throat of a venturi which, due to the sudden drop of pressure in the venturi, causes the liquid to break into small droplets of fuel. The small droplets of liquid fuel are then drawn into the cylinders of the engine for combustion.
Liquid phase fuel delivery systems, such as fuel injection, are the current standard for supplying liquid fuel to gasoline engines. Electrical pulses provided by the onboard computer cause the injectors to force liquid fuel through a nozzle. The nozzle breaks up the liquid fuel into small droplets. Some injectors aim their spray at a venturi for further atomization, others directly inject their spray into the intake manifold or combustion chamber.
While fuel injectors are generally capable of atomizing liquid fuel better than a carburetor, they still deliver the fuel in a liquid phase as small droplets of fuel. Small droplets of fuel do not burn completely during combustion causing decreased engine efficiency and increased fuel consumption. In addition, the unburned fuel is discharged into the atmosphere as a pollutant.
Devices of the prior art have attempted to overcome the problems associated with liquid phase fuel delivery systems by vaporizing the liquid fuel supplied to the engine. Fuel vaporization can be accomplished in a number of ways, including various mechanical means such as screens or venturis. Other devices use heat to vaporize the liquid fuel. The prior art contains a substantial number of suggestions directed to vaporizing liquid fuels with heat for use in an internal combustion engine. These solutions have generally centered around using the exhaust gases of the engine as a source of heat for accomplishing vaporization.
When compared to an engine operating from liquid phase fuel, an engine operating on vaporized fuel offers increased fuel economy and lower emissions. In their attempts to achieve maximum economy, the prior art has generally concentrated on operating an engine entirely on a vaporized liquid fuel such as gasoline. Because gasoline is comprised of a number of components which transform to a vapor phase at vastly different temperatures, there are a number of problems associated with vaporizing all of the components in sufficient quantities to supply a vehicle. The first such problem is an unavoidable delay associated with raising the temperature of the liquid fuel to a sufficient level to transform the fuel components with the highest boiling points to vapor. The delay adversely affects engine performance and causes poor throttle response. Numerous situations occur when operating a vehicle that require an immediate engine response time, e.g. accident avoidance and the like. While these situations only account for a small amount of total driving time, the delay associated with transforming the components of gasoline with the highest boiling temperatures to a vapor phase requires systems to be overbuilt or maintain a relatively large reserve supply of fuel vapor for acceptable operation. Overbuilt systems generally rely on excessive heat or large vaporizing apparatus to reduce response times. Reserve supplies of vaporized gasoline mixed with air are extremely volatile and may result in dangerous explosions.
A further problem associated with the overbuilt systems, that has not been adequately addressed by the prior art, involves the recognition that some gasoline components vaporize at about 95° F. while others require temperatures above 425° F. to completely vaporize. Overheating of the components with the lower boiling points may result in the formation of undesired gums and tars within the apparatus. Overheating the fuel also increases the risk of fire or explosion.
Still further problems exist with prior art systems which utilize sufficient heat to completely vaporize gasoline. When the incoming air is heated with the fuel, the heat significantly reduces air density thereby lowering the efficiency and power output of the engine. In addition, the highly heated air also results in an extremely dry air-fuel mixture. The dry air-fuel mixture does not provide adequate lubrication for the upper cylinder and the valve guides. This results in premature wear of the engine and significantly reduces its useful life.
Accordingly, what is lacking in the prior art is a cost effective multi-phase fuel system capable of separating the fuel into high volatility and low volatility components, and delivering the components to the engine in different phases to promote complete combustion and a lean air-fuel mixture. The multi-phase fuel system should achieve objectives such as providing improved efficiency, quick response, reliable engine performance, and emissions abatement. The system should include packaging flexibility for installation on various engine configurations including retrofitting existing engines with minimal modification of the original fuel system.